The present invention relates to computer graphics processing. More particularly, the present invention relates to operator interface processing, and selective visual display.
While the cathode ray tube (CRT) still accounts for a large percentage of the market for desktop displays, LCD (liquid crystal display) monitors are expected to account for a growing percentage of monitor sales. Continued widespread, if not exclusive use of LCD monitors in portable computers in addition to the growing use of LCD monitors on the desktop has fueled recent developments in display technology focusing on, for example, conventional LCD and TFT (thin-film transistor) flat-panel monitors. Further fueling the expanded use of LCD and related display technologies is a continuing drop-off in price over time.
LCD flat-panel displays have obvious advantages over desktop CRTs. For example, LCDs are generally thinner thus requiring less space, and relatively lighter, e.g. 11 lbs vs. as much as 50 lbs or even more. Due to light weight and small form factor LCD displays can be flexibly mounted in relatively small spaces. Moreover, LCD displays use nearly 75 percent less power than CRTs. Other advantages of LCD displays include the elimination of, for example, flicker, and edge distortion.
There may also however be certain problems and disadvantages associated with LCD displays. LCD displays, for example, are generally far more expensive than CRT displays. Since LCD displays often incorporate different technology in a similar form factor package, selection of the most effective technology can be challenging. A related problem with LCD displays is the data format. Most LCD displays are directly compatible with conventional analog, e.g. RGB, video graphics controllers. Some newer “digitial” LCD displays however require digital video graphics controllers having, in some cases, a proprietary output signal and proprietary connector.
Aside from compatibility issues quality issues may arise. Many contemporary LCD displays use so-called active-matrix TFT technology which generally produces a high quality display picture. Some LCD displays on the market however continue to be sold with older, passive-matrix technology, which, while generally being offered in a thin form factor, and at relatively low price, suffers from poor quality. In some cases, LCD displays are considered to be grainy and difficult to view for extended periods. Poor viewing quality in an LCD display may further result from many other factors, such as slow response time, and dimness. However, the picture quality of a typical LCD display, whether passive-matrix, active-matrix, or the like, often suffers most greatly because of the narrow viewing angle inherent in the LCD display technology. Viewing problems arise primarily due to the structure of the LCD display elements themselves along with the uniform application of intensity settings generally applied as a uniform voltage level to all pixels, which produce viewing anomalies that affect viewing quality. It should further be noted that while LCD technology conveniently illustrates problems which may arise as described herein, similar problems may arise in display technologies having similar characteristics, or whose characteristics give rise to similar problems, as will be described in greater detail hereinafter with reference to, for example, FIG. 3A and FIG. 3B.
Thus, one important problem associated with LCD displays is the dependency of image quality on the relative angel between the viewing axis and the display axis, or simply, the viewing angle as illustrated in FIG. 1A. Desktop LCD display 100 may be set at some initial angle on a desktop such that display unit surface 110 is preferably in coplanar alignment with plane 111 as seen from a side view. Accordingly, a viewing position 120 may result in a series of relative viewing angles θ0 121, θ1 122, and θ2 123 between viewing position 120 and various points on display unit surface 110 relative to plane 111. Problems may arise associated with image quality at various viewing angles θ0 121, θ1 122, and θ2 123 such that portions of an image displayed on an LCD display may appear different at points on display unit surface 110 corresponding to viewing angles θ0 121, θ1 122, and θ2 123 relative to an observer at a fixed viewing position 120.
In addition, as illustrated in FIG. 1B, to an observer positioned differently at, for example, viewing position 130, a different set of viewing angles θ0′ 131, θ1′ 132, and θ2′ 133 may cause an image on display unit 110 to appear still differently. It should further be noted that the various viewing angles are dependent on the size of display unit surface 110. For example, if display unit surface 110 is extended to include for example screen position 140, an image portion occupying screen position 140 will be observed from viewing position 130 at a viewing angle θ3 141 and the image portion may appear differently even though there is no change in display orientation.
Similar problems arise in portable or notebook computer system 200 as illustrated in FIG. 2. Notebook computer system 200 may generally include a base part 230 and a movable display part 210. As can be seen in FIG. 2, display part 210 can be tilted through a range of display orientations θ0 211, θ1 212, and θ2 213 resulting in a corresponding range of viewing angles δ0 221, δ1 222, δ2 223 relative to viewing position 220. An image presented on display part 210 will look different if the display orientation changes even when an observer maintains the same viewing position 220. Such situations may typically arise when a notebook computer system 200 is first opened and display part 210 is moved to its initial position, or when the angle associated with display part 210 angle is adjusted. As a consequence the same pixel level intensity setting will be observed differently from the same viewing position 220 as display part 210 is tilted through different angles, such as, for example, θ0 211, θ1 212, and θ2 213. It should be noted that viewing angles δ0 221, δ1 222, δ2 223 may represent either the respective angles between the plane of display part 210 or a normal to the plane of display part 210 and a line connecting the center of display part 210 with an observer's eye at viewer position 220. Since both viewing angle and display orientation are proportional they may be used interchangeably to describe, for example, tilt angle. It should be noted that for a range of fixed intensity settings each individual pixel may have a different response characteristic throughout the range of intensities based on its position with respect to the viewing position. Thus prior art approaches to tilt angle compensation, which have applied fixed intensity to all portions of the screen are still not ideally suited to correction for all pixel leves values based on a fixed viewing position and associated display orientation. Complications arise for color display systems using, for example, RGB color quantization. In such color displays, RGB composite colors at each intesity setting in the range of intensity settings possible for the disaply may be derived and rendered based on relative intensities between Red, Green, and Blue pixel components. Accordingly, for a given intensity setting, intensity variations and color distortion may occur based on viewing angle for a given pixel position with respect to viewing position. It should further be noted that as intensity settings change, color variations may be non-linear, e.g. color distortion associated with a given pixel may change throughout the range of intensity settings.
With reference to FIG. 3A, it can be observed in greater detail how, for example, orientation direction 320 with respect to normal 310 of elements 305 associated with exemplary display 300 affects the level intensity from different portions 301, and 302 of display 300 perceived, for example, at viewing position 330. It can be seen that thick arrow 340 represents a relatively high level of perceived intensity from display portion 301 corresponding to a high degree of alignment between orientation direction 320 and a line between display portion 301 and viewing position 330. Thin arrow 341 represents a relatively low level of perceived intensity from display portion 302 corresponding to a relatively low degree of alignment between orientation direction 320 and a line between display portion 301 and viewing position 330. FIG. 3B illustrates a different orientation direction 350 with respect to the same viewing position 330. It can be seen that thick arrow 360 represents a relatively high level of perceived intensity from display portion 304 corresponding to a high degree of alignment between orientation direction 350 and a line between display portion 304 and viewing position 330. Thin arrow 361 represents a relatively low level of perceived intensity from display portion 303 corresponding to a relatively low degree of alignment between orientation direction 350 and a line between display portion 303 and viewing position 330. FIG. 3B represents a problem associated with prior art intensity adjustments. In prior art display systems adjustments may be applied uniformly to display elements affecting, for example, a global alignment as illustrated by orientation direction 350 of display elements 305. While such adjustments may improve perceived pixel intensity for areas of a display which were previously obscured, other portions of the display which were relatively bright may become dim after adjustment.
Attempts that have been made to reduce the dependency of the perceived intensity of LCD displays on viewing angle. By using different display technology, for example, in plane switching (IPS) technology better viewing angles may be obtained than by using the more traditional twist nematic (TN) or super twist nematic (STN) technology, however IPS technology is less desirable since it is more expensive than TN technology. Other approaches include coating the display surface with a special layer which then acts as a spatially uniform diffuser. None of these prior art solutions however attempt to correcting an image signal to compensate for viewing angle differences before being displayed.
Thus, it can be seen that while some systems may solve some problems associated with adjusting image intensity, the difficulty posed by, for example, handling different viewing angles without resorting to more expensive technology or screen coatings remains unaddressed.
It would be appreciated in the art therefore for a method and apparatus for compensating for pixel level variations which arise due to changes in viewing angle.
It would further be appreciated in the art for a method and apparatus which automatically corrected for pixel level variations throughout a range of intensity settings.
It would still further be appreciated in the art for a method and apparatus which automatically corrected individual RGB components for pixel level variations throughout a range of intensity settings.
It would still further be appreciated in the art for a method and apparatus which automatically corrected for pixel level variations in a variety of display technologies including but not limited to LCD display technology.